1. Field of the Invention
The present invention is directed to a method and apparatus for heat treating gear teeth and more particularly to a method and apparatus to inductively heat treat beveled gear teeth.
2. Description of the Related Art
The advantages of selective surface hardening of gear teeth are well known in the art. The generic notion of inductively heat treating conventional spur gear teeth is also known in the art. Several static embodiments are known whereby a member is disposed between or adjacent gear teeth. In these devices, a member is disposed between each gear tooth, or a series of gear teeth, and a magnetic flux is induced through the gear teeth. However, each gear tooth is treated by a single and separate member resulting un-uniform treatment of the teeth. Moreover, heat treating the gear teeth individually or just a few of the gear teeth at a time is costly and time consuming.
It is also known in the art to provide a rotatable interface between an inductive heating element and a conventional spur or straight gear. However, these devices do not adequately induce a magnetic flux directly through the gear teeth. Furthermore, these prior art devices are adapted to treat conventional spur or straight gears and are not applicable for treating beveled gears. Such prior art devices are disclosed in the following U.S. Pat. Nos.: 3,555,233; 3,236,993; 2,424,816; 2,398,085; 2,390,559; and 2,364,623 which are each incorporated herein by reference.
Heretofore, inductive heat treatment of bevel gear teeth has been limited to a fixed flat inductor coil simply positioned adjacent the beveled gear. However, these devices have a gap between the coil and the root of the tooth. Such devices fail to provide adequate treatment in the root area of the tooth thus reduce case depth treatment. Such a drawback results in weaker gears. None of the prior art devices provides a mechanism for uniformly induction heating beveled gear teeth or so treating beveled gears to reach sufficient case depth in the root area of the tooth.
The present invention is directed to apparatus and method of heat treating beveled gear teeth that both provide uniform treatment and sufficient case depth in the root are of the tooth. An inductor has an annular body with a plurality of projections closely resembling the profile of the beveled gear teeth for meshingly engaging the bevel gear. An inductor coil or loop is associated with each of the projections or other means to generate a magnetic flux around each projection. The projections are adapted to be at least partially disposed between successive gear teeth to induce a magnetic flux directly there through when engaging the beveled gear. By simply rotating the inductor relative to the beveled gear while simultaneously sending a current through the coil, successive gear teeth are treated. Because magnetic flux is generated around the projections within and between each gear teeth, the case depth of the induction heat treatment is increased to the root area of the tooth. Furthermore, the number of gear teeth differs from the number of projections, and the beveled gear is rotated sufficiently to ensure that each of the projections and associated coil engages each of the beveled gear teeth to facilitate a more uniform treatment.